1. Area of the Art
The present invention concerns the art of fluidics and particularly microfluidics.
2. Description of the Background Art
Microfluidics involves miniature fluid devices; the art is often defined as the art of dealing with small fluidic volumes (sub-milliliter volumes) typically in channels having at least one dimension less than one millimeter. Of course, this definition is flexible and the present invention can be useful in devices with different configurations and different sizes. In fact, there are microfluidic devices having no confinement channels at all. Typical microfluidic devices have micromechanical structures (microchannel, microvalves and others) and employ various fluid-moving means, such as mechanical parts (e.g., micropumps) hydro-pneumatic devices/methods and electrically-based effects (electrophoretic, dielectrophoretic, electro-osmotic, electrowetting, opto-electrowetting, variations of these effects as well as other effects).
For biomedical applications, some microfluidic devices are designed to conduct sample processing, including concentration, filtration, washing, dispensing, mixing, transport, sample splitting, sample lysing and other sample handling functions. Biomolecular adsorption is a problem for microfluidic devices in that the surfaces that are exposed to the sample liquids during sample handling, processing or sensing can become “fouled” by the adsorption of various biomolecules. Changes in surface properties due to unwanted surface adsorption of biomolecules can lead to cross contamination, loss of target molecules availability for sensing, degradation of sensing surfaces, and/or degradation in the passive and active control of surface effects, valving and other mechanical effects needed for sample processing.
One established method of mitigating biomolecular adsorption is to pretreat or coat the surface of the microfluidic device with a blocking agent prior to sample handling. For example, “Pegylation” involves the precoating of microfluidic surfaces with Poly-Ethylene-Glycol (PEG) to block non-specific adsorption during sample handling. Reactive derivatives of PEG can be used to ensure covalent bonding to the surface. Additional blocking agents include a variety of generally hydrophilic substances including large molecules like common proteins as well as smaller molecules which can include carboxylic acid derivatives, carbohydrates and even silicon containing compounds. While surfaces can be “Pegylated” (including treatment with other blocking agents) through passive absorption of the blocking agent, it is generally preferred to effect a covalent linkage of the blocking agent and the surface.
One possible drawback of pretreatment or pre-coating a microfluidic device to prevent non-specific binding is that such a treatment leads to permanent changes in the surface characteristics and may impede active control over surface effects (adsorption, wettability, etc.) needed to achieve local and intermittent sample processing effects. Another drawback to precoating with blocking agents is that a specific blocking agent or surface coating may be required for a particular sample liquid or molecule, thus rendering the device unusable for other sample molecules or sample liquid formulations.